Organic light emitting display

ABSTRACT

An organic light emitting display (OLED) is disclosed. The OLED includes a storage capacitor formed in a first region of the substrate, a thin film transistor formed in a second region of the substrate, a first data line capacitor formed in a third region of the substrate, an organic light emitting diode formed on the storage capacitor and the thin film transistor, and a second data line capacitor formed on the data line capacitor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims priority to U.S.application Ser. No. 13/007,371, filed Jan. 14, 2011 which is adivisional of U.S. application Ser. No. 11/432,598, filed May 11, 2006,which claims priority to and the benefit of Korean Patent ApplicationNo. 10-2005-0039895, filed May 12, 2005, each of which is incorporatedherein by reference in its entirety. Any and all applications for whicha foreign or domestic priority claim is identified in the ApplicationData Sheet as filed with the present application are hereby incorporatedby reference under 37 CFR 1.57.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic light emitting display(OLED), and more particularly, to an OLED that makes use ofdemultiplexers to decrease the number of output lines of data driversand display an image having uniform luminance.

2. Description of the Related Art

In recent years, a variety of flat panel displays (FPDs) with smallweight and volume have been developed to overcome the drawbacks of acathode ray tube (CRT). The FPDs can be categorized into a liquidcrystal display (LCD), a field emission display (FED), a plasma displaypanel (PDP), an organic light emitting display (OLED), and the like.

An OLED includes an organic light emitting diode, which is aself-emissive display device that emits light through the recombinationof electrons supplied from a cathode and holes supplied from an anode.The OLED has a high response speed of about 1 μs and consumes low power.The OLED includes a plurality of pixels, each of which supplies adriving current corresponding to a data signal to the organic lightemitting diode using a driving thin film transistor (TFT) so that theorganic light emitting diode emits light to display a predeterminedimage.

FIG. 1 is a block diagram of a conventional OLED.

Referring to FIG. 1, the conventional OLED includes a display panel 10,a scan driver 20, a data driver 30, and a timing controller 40.

The display panel 10 includes a plurality of pixels P₁₁-P_(nm), whichare disposed in regions where a plurality of scan lines and emissioncontrol lines S₁-S_(n) and E₁-E_(n) intersect a plurality of data linesD₁-D_(m). Each of the pixels P₁₁-P_(nm) receives a first power supplyVdd and a second power supply Vss from external power supplies and emitslight corresponding to a received data signal to display an image. Also,the pixels P₁₁-P_(nm) emit light for a time that is controlled accordingto a signal supplied through the emission control lines E₁-E_(n),respectively.

The scan driver 20 generates a scan signal in response to a scan controlsignal S_(g) received from the timing controller 40 and sequentiallytransmits the generated scan signal to the plurality of scan linesS₁-S_(n) to select the pixels P₁₁-P_(nm). Also, the scan driver 20generates an emission control signal in response to the scan controlsignal S_(g) and sequentially transmits the generated emission controlsignal to the plurality of emission control lines E₁-E_(n) to controlthe emission.

The data driver 30 receives red (R), green (G), and blue (B) data fromthe timing controller 40, generates data signals in response to a datacontrol signal S_(d), and transmits the generated data signals to theplurality of data lines D₁-D_(m). In this case, the data driver 30transmits data signals corresponding to one horizontal line for eachhorizontal period to the plurality of data lines D₁-D_(m).

The timing controller 40 generates data control signals S_(d) and scancontrol signals S_(g) corresponding to R, G, and B data supplied from anexternal graphic controller (not shown) and horizontal and verticalsynchronous signals Hsync and Vsync. The data control signals S_(d) andthe scan control signals S_(g) generated by the timing controller 40 aresupplied to the data driver 30 and the scan driver 20, respectively.

In the conventional OLED having the above-described construction, therespective pixels P₁₁-P_(nm) are located in the regions where the scanlines and the emission control lines S₁-S_(n) and E₁-E_(n) intersect thedata lines D₁-D_(m). Here, the data driver 30 includes m output linessuch that it transmits data signals to each of the m data linesD₁-D_(m). In other words, the data driver 30 should include the outputlines in a number equal to the number of the data lines D₁-D_(m).Accordingly, the data driver 30 should include a plurality of dataintegrated circuits (ICs) to install the m output lines, thus elevatingthe cost of production. In particular, as the display panel 10 increasesin resolution and size, the data driver 30 should include more data ICs.Thus, the cost of production further increases.

SUMMARY OF THE INVENTION

The present invention, therefore, provides an organic light emittingdisplay (OLED), which makes use of demultiplexers to decrease the numberof data drivers and display an image having uniform luminance.

One embodiment comprises an organic light emitting display (OLED)including a display panel having a plurality of pixels disposed inregions where a plurality of scan lines intersect a plurality of datalines, a scan driver configured to supply scan signals to the scan linesso as to select the pixels, a plurality of demultiplexers configured tosupply data signals to the data lines, a data driver configured tosupply the data signals to a plurality of output lines connected to thedemultiplexers, and a plurality of data line capacitors each disposed inone of the data lines and configured to store a voltage corresponding tothe data signal.

Another embodiment comprises an organic light emitting display (OLED)including a substrate, a storage capacitor region, a thin filmtransistor region, and a data line capacitor region each formed on thesubstrate. The OLED also has a storage capacitor formed in the storagecapacitor region, the storage capacitor including a first semiconductorlayer formed on the substrate, a gate insulating layer formed on thefirst semiconductor layer, a first electrode formed on the gateinsulating layer, an interlayer insulating layer formed on the firstelectrode, and a second electrode formed on the interlayer insulatinglayer, where the second electrode is electrically connected to the firstsemiconductor layer. The OLED also has a thin film transistor formed inthe thin film transistor region, the thin film transistor including asecond semiconductor layer formed on the substrate, a gate insulatinglayer formed on the second semiconductor layer. The OLED also has a gateelectrode formed on the gate insulating layer, a source electrode formedon the gate insulating layer, and a drain electrode formed on the gateinsulating layer, and a first data line capacitor formed in the dataline capacitor region, the first data line capacitor including a thirdsemiconductor layer formed on the substrate, a gate insulating layerformed on the third semiconductor layer, an interlayer insulating layerformed on the gate insulating layer, and a data line formed on theinterlayer insulating layer. The OLED also has an organic light emittingdiode formed on the storage capacitor and the thin film transistor andincluding a pixel electrode connected to one of the source and drainelectrodes, an organic emission layer formed on the pixel electrode, andan opposite electrode formed on the storage capacitor, the thin filmtransistor, and the first data line capacitor. The OLED also has asecond data line capacitor formed on the data line capacitor, the seconddata line capacitor including the data line, an insulating layer formedover the data line, and the opposite electrode.

Another embodiment comprises an organic light emitting display (OLED)including a substrate, a storage capacitor region, a thin filmtransistor region, and a data line capacitor region each formed on thesubstrate. The OLED also has a storage capacitor formed in the storagecapacitor region, the storage capacitor including a first semiconductorlayer formed on the substrate, a gate insulating layer formed on thefirst semiconductor layer, a first electrode formed on the gateinsulating layer, an interlayer insulating layer formed on the firstelectrode, and a second electrode formed on the interlayer insulatinglayer, where the second electrode is electrically connected to the firstsemiconductor layer. The OLED also has a thin film transistor formed inthe thin film transistor region, the thin film transistor including asecond semiconductor layer formed on the substrate, a gate insulatinglayer formed on the second semiconductor layer. The OLED also has a gateelectrode formed on the gate insulating layer, a source electrode formedon the gate insulating layer, and a drain electrode formed on the gateinsulating layer, and a first data line capacitor formed in the dataline capacitor region, the first data line capacitor including a thirdsemiconductor layer formed on the substrate, a gate insulating layerformed on the third semiconductor layer, an interlayer insulating layerformed on the gate insulating layer, and a data line formed on theinterlayer insulating layer. The OLED also has an organic light emittingdiode formed on the storage capacitor and the thin film transistor andincluding a pixel electrode connected to one of the source and drainelectrodes, an organic emission layer formed on the pixel electrode, andan opposite electrode formed on the storage capacitor, the thin filmtransistor, and the first data line capacitor. The OLED also has asecond data line capacitor formed on the data line capacitor, the seconddata line capacitor including the data line, an insulating layer formedover the data line, and the pixel electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of certain inventive aspectsare discussed with further detail with reference to the attacheddrawings in which:

FIG. 1 is a block diagram of a conventional organic light emittingdisplay (OLED);

FIG. 2 is a block diagram of an OLED according to an exemplaryembodiment;

FIG. 3 is a circuit diagram of a demultiplexer shown in FIG. 2;

FIG. 4 is a circuit diagram of one of N×M pixels shown in FIG. 2;

FIG. 5 is a detailed circuit diagram showing connection of thedemultiplexer to the pixels shown in FIG. 2;

FIG. 6 is a timing diagram illustrating operations of the pixel circuitshown in FIG. 5;

FIG. 7 is a graph of simulation results showing gate voltages of adriving transistor versus capacitances of a data line capacitor and astorage capacitor of a pixel in the OLED;

FIG. 8 is a cross-sectional view of a pixel having a structure toincrease the capacitance of a data line capacitor according to oneembodiment;

FIG. 9 is a cross-sectional view of a pixel having a structure toincrease the capacitance of a data line capacitor according to anotherembodiment;

FIG. 10 is a cross-sectional view of a pixel having a structure toincrease the capacitance of a data line capacitor according to yetanother embodiment;

FIG. 11 is a cross-sectional view of a pixel having a structure toincrease the capacitance of a data line capacitor according to stillanother embodiment;

FIG. 12 is a circuit diagram of another pixel of the OLED shown in FIG.2;

FIG. 13 is a circuit diagram of yet another pixel of the OLED shown inFIG. 2; and

FIG. 14 is a circuit diagram of still another pixel of the OLED shown inFIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 is a block diagram of an organic light emitting display (OLED)according to one embodiment of the present invention.

Referring to FIG. 2, the OLED includes a display panel 100, a scandriver 120, a data driver 130, a timing controller 140, a demultiplexerunit 150, and a demultiplexer controller 160.

The display panel 100 includes a plurality of pixels P₁₁₁-P_(nmk) and aplurality of data line capacitors C_(data11)-C_(datamk). The pixelsP₁₁₁-P_(nmk) are disposed in a region that comprises a plurality of scanlines and emission control lines S₁-S_(n) and E₁-E_(n) and a pluralityof data lines D₁₁-D_(mk). Also, the data line capacitorsC_(data11)-C_(datamk) are formed by the respective data linesD₁₁-D_(mk).

Each of the pixels P₁₁₁-P_(nmk) emits light corresponding to a datasignal applied from one of the data lines D₁₁-D_(mk). A pixel 110, whichis representative of the pixels P₁₁₁-P_(nmk), will be described later.

Also, the plurality of data line capacitors C_(data11)-C_(datamk) areformed by each of the data lines D₁₁-D_(mk) in order to store the datasignal temporarily. For example, the data line capacitor C_(data11) ofthe data line D₁₁ is formed by connecting in parallel all of the dataline capacitors C_(data111), C_(data211), . . . , and C_(datan11), whichare formed in the regions where the pixels P₁₁₁, P₂₁₁, . . . , andP_(n11) connect to the data line D₁₁. That is, it can be expressed thatC_(data11)=C_(data111)+C_(data211)+ . . . C_(datan11).

For example, during a data writing period, when a data signal is appliedto the first data line D₁₁ to make the first pixel P₁₁₁ emit light, thedata signal is temporarily stored in the first data line capacitorC_(data11) formed in the data line D₁₁. Next, during a scan period, oncethe first pixel P₁₁₁ is selected by a first scan signal S₁, the datavoltage stored in the first data line capacitor C_(data11) is applied tothe first pixel P₁₁₁ so that the first pixel P₁₁₁ emits lightcorresponding to the data voltage. In other words, the data linecapacitors C_(data11)-C_(datamk) formed in each of the data linesD₁₁-D_(mk) temporarily store the data signal applied to the data linesD₁₁-D_(mk) and apply the stored data voltages to the pixels P₁₁₁-P_(nmk)selected by the appropriate scan signal. Here, the data line capacitorsC_(data11)-C_(datamk) make use of parasitic capacitors that are formedby the data lines D₁₁-D_(mk), an electrode, and an insulating layerinterposed therebetween. Actually, the capacitance of each of the dataline capacitors C_(data11)-C_(datamk) that are equivalently formed inthe data lines D₁₁-D_(mk) may be greater than the capacitance of astorage capacitor C_(st) included in each of the pixels P₁₁₁-P_(nmk) inorder to stably store the data signal. In some embodiments, the dataline capacitors C_(data11)-C_(datamk) have capacitance of about 20 pF toabout 50 pF.

The scan driver 120 generates a scan signal in response to scan controlsignals S_(g) applied from the timing controller 140 and sequentiallytransmits the scan signal to the scan lines S₁-S_(n). Here, the scandriver 120 transmits the scan signal to each scan line only during apartial period (i.e., a scan period) of one horizontal period 1H asshown in FIG. 6. More specifically, one horizontal period 1H is dividedinto a scan period and a data writing period. The scan driver 120transmits a scan signal to the scan line S during the scan period of theone horizontal period 1H but does not transmit the scan signal duringthe data writing period. Additionally, the scan driver 120 generates anemission control signal in response to the scan control signals S_(g)and sequentially transmits the emission control signal to the emissioncontrol lines E₁-E_(n) to control the emission operation.

The data driver 130 receives R, G, and B data from the timing controller140 and sequentially transmits R, G, B data signals to output linesD₁-D_(m) in response to data control signals S_(d). During the datawriting period, the data driver 130 sequentially transmits k (k is anintegral number equal to or more than 2) data signals (but, FIG. 6illustrates only R, G, B data signals). More specifically, the datadriver 130 sequentially transmits data signals (e.g., R, G, and B data),which will be supplied to corresponding pixels during a data writingperiod of the one horizontal period 1H. In this case, since the datasignals R, G, and B, which will be supplied to the corresponding pixels,are supplied only during the data writing period, the data writingperiod does not overlap the scan period for which scan signals aresupplied.

The timing controller 140 generates the data control signals S_(d) andthe scan control signals S_(g) corresponding to R, G, and B datasupplied from an external graphic controller (not shown) and horizontaland vertical synchronous signals. The data control signals S_(d) and thescan control signals S_(g), which are generated by the timing controller140, are supplied to the data driver 130 and the scan driver 120,respectively.

The demultiplexer unit 150 includes m demultiplexers 151. Specifically,the demultiplexer unit 150 includes the demultiplexers 151 in a numberequal to the number of the output lines D₁-D_(m) connected to the datadriver 130. The demultiplexers 151 have input terminals connected to theoutput lines D₁-D_(m), respectively, and have output terminals connectedto the m×k data lines D₁₁-D_(mk). Each of the demultiplexers 151 drive kdata signals, to the k data lines to which they are each connected.Because of the demultiplexers, the number of output lines included inthe data driver 130 is sharply reduced. For example, assuming that k is3, the number of output lines included in the data driver 130 is reducedto about ⅓ as many as in the conventional case, thus the number of dataintegrated circuits (ICs) included in the data driver 130 is alsoreduced. In the present invention, the data signals, which are suppliedto one output line D₁, are supplied to the k data lines D₁₁-D_(1k) usingthe demultiplexers 151, so that the fabrication cost of the data ICs canbe greatly reduced.

The demultiplexer controller 160 transmits k control signals to controlterminals of the demultiplexers 151, during the data writing period ofthe one horizontal period 1H, such that the k data signals are eachdriven onto the correct data line of the k data lines D₁₁-D_(1k). Inthis case, the k data signals, which are supplied from the demultiplexercontroller 160, are sequentially supplied so as to not overlap oneanother during the data writing period as shown in FIG. 6. Meanwhile,although it is illustrated in FIG. 2 that the demultiplexer controller160 is installed separate from the timing controller 140, in otherembodiments the demultiplexer controller 160 may be integrated with thetiming controller 140.

FIG. 3 is a circuit diagram of an embodiment of one of thedemultiplexers shown in FIG. 2.

In the embodiment of FIG. 3, k is 3 for. Also, the demultiplexer shownin FIG. 3 is connected to the first output line D₁ of the data driver130.

Referring to FIG. 3, the demultiplexer 151 includes a first switchingdevice T₁, a second switching device T₂, and a third switching deviceT₃. Each of the switching devices T₁, T₂, and T₃ may be formed of a thinfilm transistor (TFT). In this embodiment, each of the switching devicesT₁, T₂, and T₃ is formed of a p-type metal oxide semiconductor fieldeffect transistor (MOSFET), however, in other embodiments they may beformed of an n-type MOSFET, or another type of switching element.

The first switching device T₁ is connected between the first output lineD₁ and the first data line D₁₁. The first switching device T₁ is turnedon when a first control signal CS1 is supplied from the demultiplexercontroller 160 and transmits the data signal, which is supplied from thefirst output line D₁, to the first data line D₁₁. The data signalsupplied to the first data line D₁ is stored in the first data linecapacitor C_(data11) during the data writing period as described abovewith reference to FIG. 2.

The second switching device T₂ is connected between the first outputline D₁ and the second data line D₁₂. The second switching device T₂ isturned on when a second control signal CS2 is supplied from thedemultiplexer controller 160 and transmits the data signal, which issupplied from the first output line D₁, to the second data line D₁₂. Thedata signal supplied to the second data line D₁₂ is stored in the seconddata line capacitor C_(data12) during the data writing period asdescribed above with reference to FIG. 2.

The third switching device T₃ is connected between the first output lineD₁ and the third data line D₁₃. The third switching device T₃ is turnedon when a third control signal CS3 is supplied from the demultiplexercontroller 160 and transmits the data signal, which is supplied from thefirst output line D₁, to the third data line D₁₃. The data signalsupplied to the third data line D₁₃ is stored in the third data linecapacitor C_(data13) during the data writing period as described abovewith reference to FIG. 2. The operations of the demultiplexers 151 willbe described in detail later along with the construction of the pixel110.

FIG. 4 is a circuit diagram of one of the n×m×k pixels shown in FIG. 2.Here, a pixel according to an one embodiment is shown, but other pixelsmay also be used.

Referring to FIG. 4, the pixel 110 includes an organic light emittingdiode OLED and a pixel driving circuit 111, which is connected to a dataline D_(mk), scan lines S_(n) and S_(n-1), an emission control lineE_(n), a first voltage line Vdd, and an initialization voltage lineVinit and generates a driving current for the organic light emittingdiode OLED. A data line capacitor C_(data mk) is formed in the data lineD to store a data voltage for the pixel 110.

The organic light emitting diode OLED has an anode connected to thepixel driving circuit 111 and a cathode connected to a second powersupply line Vss. A second power supply Vss may be a voltage lower than afirst power supply Vdd, for example, a ground or negative (−) voltage.The organic light emitting diode OLED emits light corresponding to thedriving current supplied from the pixel driving circuit 111.

The pixel driving circuit 111 includes a storage capacitor C_(st) andsix transistors M1-M6. Here, the first transistor M1 is a drivingtransistor, the third transistor M3 is a threshold voltage compensationtransistor for diode-connecting the first transistor M1 to compensatefor a threshold voltage, and the fourth transistor M4 is aninitialization transistor for initializing the storage capacitor C_(st).Also, the sixth transistor M6 is an emission control transistor forcontrolling the emission of the organic light emitting diode OLED, andthe second and fifth transistors M2 and M5 are switching transistors.

The second switching transistor M2 has a gate electrode connected to annth scan line S_(n) and a source electrode connected to the data line D.The second switching transistor M2 is turned on in response to a scansignal transmitted through the nth scan line S_(n) and transmits a datavoltage applied from the data line capacitor C_(data mk).

The driving transistor M1 has a source electrode connected to a drainelectrode of the second switching transistor M2 and a gate electrodeconnected to a node N. A source or drain electrode of the thresholdvoltage compensation transistor M3 and a first terminal of the storagecapacitor C_(st) are also connected to the node N, so that a gatevoltage of the driving transistor M1 is the same as voltage of the nodeN. Thus, the driving transistor M1 generates a driving currentcorresponding to the voltage applied to its gate electrode.

The threshold voltage compensation transistor M3 is connected betweenthe gate and source electrodes of the driving transistor M1 anddiode-connects the driving transistor M1 in response to the scan signaltransmitted through the nth scan line S_(n). Thus, the drivingtransistor M1 functions as a diode in response to the scan signal sothat a voltage Vdata−Vth[V] is applied to the node N and becomes thegate voltage of the driving transistor M1.

The initialization transistor M4 is connected between the initializationpower supply line Vinit and the first terminal of the storage capacitorC_(st). The initialization transistor M4 discharges electric charges,which are charged in the storage capacitor C_(st) during the previousframe period, through the initialization power supply line Vinit inresponse to a scan signal supplied through the (n−1)th scan line S_(n-1)connected to the gate electrode, so that the storage capacitor C_(st)can be initialized.

The fifth switching transistor M5 is connected between the first powersupply line Vdd and the source electrode of the driving transistor M1.The fifth switching transistor M5 is turned on in response to anemission control signal supplied through the nth emission control lineE_(n) connected to the gate electrode and supplies the first powersupply Vdd to the source electrode of the driving transistor M1.

The emission control transistor M6 is connected between the drivingtransistor M1 and the organic light emitting diode OLED. The emissioncontrol transistor M6 transmits the driving current, which is generatedby the driving transistor M1, to the organic light emitting diode OLEDin response to an emission control signal supplied through the nthemission control line E_(n) connected to the gate electrode.

The storage capacitor C_(st) is connected between the first power supplyline Vdd and the gate electrode of the driving transistor M1. Thestorage capacitor C_(st) maintains electric charges so as to maintain avoltage difference between the first power supply Vdd and the voltageVdata−Vth[V] applied to the gate electrode of the driving transistor M1,during one frame period.

Although it is illustrated in FIG. 4 that each of the transistors M1-M6is a p-type MOSFET, each of the transistors M1-M6 can instead bedesigned as an N-type MOSFET.

FIG. 5 is a detailed circuit diagram showing the connection of thedemultiplexer with the pixels shown in FIG. 2, and FIG. 6 is a timingdiagram illustrating operations of a pixel circuit shown in FIG. 5.Here, red (R), green (G), and blue (B) pixels are connected to thedemultiplexers 151 which is connected to the first output line D1 (i.e.,k=3).

Referring to FIGS. 5 and 6, a low-level scan signal is applied to the(n−1)th scan line S_(n-1) during an (n−1)th scan period of onehorizontal period 1H. Once the scan signal is applied to the (n−1)thscan line S_(n-1), the initialization transistor M4, which is includedin each of the R, G, and B pixels, is turned on. When the initializationtransistor M4 is turned on, one terminal of the storage capacitor C_(st)and a gate terminal of the driving transistor M1 are connected to theinitialization power supply line Vinit. That is, when the scan signal isapplied to the (n−1)th scan line S_(n-1), a data voltage of the previousframe stored in the storage capacitor C_(st) of each of the R, G, and Bpixels, i.e., the gate voltage of the driving transistor M1, isinitialized. When the scan signal is applied to the (n−1)th scan lineS_(n-1), the first switching transistor M2 connected to the nth scanline S_(n) remains turned off.

Thereafter, the first switching device T₁, the second switching deviceT₂, and the third switching device T₃ are sequentially turned on inresponse to the first through third control signals CS1, CS2, and CS3that are sequentially supplied during the data writing period.Initially, when the first switching device T₁ is turned on in responseto the first control signal CS1, an R data signal supplied to the firstoutput line D₁ is applied to the first data line D₁₁. In this case, thefirst data line capacitor C_(data11) is charged with a voltagecorresponding to the R data signal applied to the first data line D₁₁.Next, the second switching device T₂ is turned on in response to thesecond control signal CS2, thus a G data signal supplied to the firstoutput line D1 is applied to the second data line D₁₂. In this case, thesecond data line capacitor C_(data12) is charged with a voltagecorresponding to the G data signal applied to the second data line D₁₂.Finally, the third switching device T₃ is turned on in response to thethird control signal CS3, thus a B data signal supplied to the firstoutput line D₁ is applied to the third data line D₁₃. In this case, thethird data line capacitor C_(data13) is charged with a voltagecorresponding to the B data signal applied to the third data line D₁₃.Meanwhile, since no scan signal is applied to the nth scan line S_(n)during the data writing period, the R, G, and B data signals are notsupplied to the R, G, and B pixels.

Thereafter, a low-level scan signal is applied to the nth scan lineS_(n) during an nth scan period that follows the data writing period.Once the scan signal is applied to the nth scan line S_(n), the firstswitching transistor M2 and the threshold voltage compensationtransistor M3 which are included in each of the R, G, and B pixels areturned on. The first switching transistor M2 of each of the R, G, and Bpixels transmits a voltage Vdata corresponding to the R, G, and B datasignals, which are stored in the first through third data linecapacitors C_(data11)-C_(data13) in the data writing period, to the R,G, and B pixels. The threshold voltage compensation transistor M3 servesto diode-connect the driving transistor M1. That is, a voltageVdata−Vth_(M1)[V] corresponding to a difference between the voltageVdata corresponding to the R, G, and B data signals stored in the firstthrough third data line capacitors C_(data11)-C_(data13) and a thresholdvoltage Vth of the driving transistor M1 is applied to the gate terminalof the driving transistor M1 and one terminal of the storage capacitorC_(st) through the diode-connected driving transistor M1.

Thereafter, a low-level emission control signal is applied to theemission control line En. Thus, both the fifth switching transistor M5and the emission control transistor M6 are turned on, so that a drivingcurrent corresponding to the first power supply Vdd applied to thesource terminal of the driving transistor M1 and the voltageVdata-Vth_(M1) applied to its gate terminal is supplied to the organiclight emitting diode OLED through the emission control transistor M6.Thus, the organic light emitting diode OLED emits light with a luminancecorresponding to the data.

In this case, the driving current supplied to the organic light emittingdiode OLED can be expressed as Equation 1:

I _(OLED) =K(Vgs _(M1) −Vth _(M1))² =K(Vdd−Vdata+Vth _(M1) −Vth _(M1))²=K(Vdd−Vdata)²  (1)

where I_(OLED) is the current that flows through the organic lightemitting diode OLED, Vgs_(M1) is the voltage between the source and gateelectrodes of the first transistor M1, Vth_(M1) is the threshold voltageof the first transistor M1, Vdata is the data voltage, Vdd is the firstvoltage, and K is a constant.

As can be seen from Equation 1, the driving current corresponding to thefirst power supply voltage Vdd and the R, G, and B data voltages Vdatastored in the data line capacitors C_(data11), C_(data12), andC_(data13) of the data lines D11, D12, and D13 flows through the organiclight emitting diode OLED irrespective of the threshold voltage Vth_(M1)of the driving transistor M1. In other words, a pixel according to anexemplary embodiment of the present invention detects a variance of thethreshold voltage Vth_(M1) of the driving transistor M1 using thethreshold voltage compensation transistor M3 and compensates for thevariance on its own, thereby improving the non-uniformity of luminanceresulting from the variance of the threshold voltage Vth_(M1).

Accordingly, the OLED is advantageous in supplying R, G, and B datasignals, which are sequentially applied to the first output line D1, tothe k data lines D₁₁-D_(1k) using the demultiplexers 151. Also, voltagescorresponding to data signals are stored in the data line capacitorsC_(data11)-C_(data1k) during the data writing period, and the voltagesstored in the data line capacitors C_(data11)-C_(data1k) are applied topixels during the scan period. Since the voltages stored in the dataline capacitors C_(data11)-C_(data1k) are simultaneously applied to therespective pixels, i.e., since the respective data signals are suppliedat the same point in time, an image with uniform luminance can bedisplayed.

However, as one horizontal period 1H is divided into the scan period andthe data writing period, the data line capacitor C_(datamk) and thestorage capacitor C_(st) included in each of the pixels, which areseparated during the data writing period, are connected to each otherduring the scan period. Thus, electric charges equivalent to the datavoltage Vdata stored in the data line capacitor C_(datamk) are sharedbetween the capacitors C_(datamk) and C_(st), so that the gate voltageVgM1 of the driving transistor M1 is substantially given by:

$\begin{matrix}{{{VgM}\; 1} = \frac{{CdatasVdata} + {{Csts}( {{Vinit} - {Vdd}} )}}{( {{Cdata} + {Cst}} )}} & (2)\end{matrix}$

where Vg_(M1) is the gate voltage of the driving transistor M1, Vdata isthe data voltage, Vinit is the initialization voltage, Vdd is the firstpower supply, C_(data) is the data line capacitor, and C_(st) is thestorage capacitor included in each of the pixels.

As can be seen from Equation 2, there may be a difference between thegate voltage Vg_(M1) of the driving transistor M1 and the data voltageVdata applied according to the capacitances of the data line capacitorC_(data) and the storage capacitor C_(st) included in each of thepixels. Because of the difference between the applied data voltage Vdataand the gate voltage Vg_(M1), the luminance of the OLED may becomenon-uniform.

FIG. 7 is a graph of simulation results showing gate voltages of adriving transistor versus capacitances of a data line capacitor and astorage capacitor of a pixel. In FIG. 7, it is assumed that the datavoltage Vdata applied to each pixel of FIG. 5 is 3 [V].

Referring to FIG. 7, the simulation results were obtained by measuringthe gate voltage Vg_(M1) of the driving transistor M1 while setting thecapacitance of the storage capacitor C_(st) included in the pixel to0.2, 0.4, 0.6, 0.8, and 1 [PF] and varying the capacitance of the dataline capacitor C_(data) from 5 to 50 [PF].

In applying a data voltage Vdata of 3[V] to the data line, when thecapacitance of the data line capacitor C_(data) was 5 [PF], the gatevoltage Vg_(M1) of the driving transistor M1 was 2, 2.35, and 2.75[V]when the capacitance of the storage capacitor C_(st) included in thepixel was 1, 0.6, and 0.2[PF], respectively.

However, as the capacitance of the data line capacitor C_(data) wasincreased to 20 [PF], the gate voltage Vg_(M1) of the driving transistorM1 was 2.7, 2.85, and 2.94[V] when the capacitance of the storagecapacitor C_(st) included in the pixel was 1, 0.6, and 0.2 [PF],respectively. That is, the gate voltage Vg_(M1) of the drivingtransistor M1 was generally increased higher than when the capacitanceof the data line capacitor C_(data) was 5 [PF].

Also, as the capacitance of the data line capacitor C_(data) wasincreased to 50 [PF], the gate voltage Vg_(M1) of the driving transistorM1 was 2.89, 2.93, and 2.98[V] when the capacitance of the storagecapacitor C_(st) included in the pixel was 1, 0.6, and 0.2 [PF],respectively. That is, the gate voltage Vg_(M1) of the drivingtransistor M1 was generally increased higher than when the capacitanceof the data line capacitor C_(data) was 20[PF]. Accordingly, based onthe simulation results of FIG. 7, it can be concluded that when the dataline capacitor C_(data) has much greater capacitance than the storagecapacitor C_(st) of the pixel, the gate voltage Vg_(M1) of the drivingtransistor M1 is equal or close to the applied data voltage Vdata. Thatis, in the pixel to which the data voltage Vdata is applied using thedemultiplexer of FIG. 5 according to the timing diagram of FIG. 6, thecapacitance of the data line capacitor C_(data) may be about 20 to50[PF]. In this case, the applied data voltage Vdata becomes almostequal to the gate voltage Vg_(M1) of the driving transistor M1 so thatthe OLED has uniform luminance.

Processes of fabricating pixels for substantially elevating thecapacitance of the data line capacitor C_(data) to 20 to 50 [PF] willnow be described with reference to cross-sectional views of FIGS. 8through 11.

FIG. 8 is a cross-sectional view of a pixel having a structure toincrease the capacitance of a data line capacitor according to oneembodiment. In FIG. 8, a pixel region is divided into 3 regions, i.e., aTFT region (a), a data line capacitor region (b), and a storagecapacitor region (c). The TFT region (a) supplies a driving current toan organic light emitting diode. The data line capacitor region (b)receives a data voltage during the data writing period and temporarilystores the data voltage. Also, the storage capacitor region (c) storesthe data voltage for a predetermined time during an nth scan period.

Referring to FIG. 8, a substrate 200 is prepared to form the pixelregion according to one embodiment. The substrate 200 may be atransparent or opaque substrate. Also, the substrate 200 may comprise atleast one of glass, plastic, quartz, silicon and metal.

A buffer layer 205 may be formed on the substrate 200. The buffer layer205 may comprise at least one of a silicon oxide (SiO₂) layer, a siliconnitride (SiN_(X)) layer, a silicon oxynitride (SiO₂N_(X)) layer, and amulti-layer thereof.

First through third semiconductor layers 207, 208, and 209 are patternedon the buffer layer 205. That is, the first semiconductor layer 207 ispatterned in the storage capacitor region (c), the second semiconductorlayer 208 is patterned in the TFT region (a), and the thirdsemiconductor layer 209 is patterned in the data line capacitor region(b). The first through third semiconductor layers 207, 208, and 209 maybe amorphous silicon (a-Si) layers or polysilicon silicon (poly-Si)layers obtained by crystallizing the a-Si layers. In some embodiments,the first through third semiconductor layers 207, 208, and 209 arepoly-Si layers having high charge mobility.

A gate insulating layer 210 is formed over the entire surface of thesubstrate 200 including the first through third semiconductor layers207, 208, and 209. The gate insulating layer 210 may comprise at leastone of a silicon oxide (SiO₂) layer, a silicon nitride (SiN_(X)) layer,a silicon oxynitride (SiO₂N_(X)) layer, and a multi-layer thereof.

A first electrode 212 of a storage capacitor C_(st) is formed on thegate insulating layer 210 in the storage capacitor region (c) to overlapthe first semiconductor layer 207, and a gate electrode 214 is formed onthe TFT region (a) to overlap the second semiconductor layer 208. Inthis case, while the first electrode 212 and the gate electrode 214 arebeing formed, scan lines (S_(n-1), S_(n), and E_(n) of FIG. 4) can beformed at the same time.

Thereafter, dopants (n⁺ or p⁺ type) are implanted into the secondsemiconductor layer 208 in the TFT region (a) using the gate electrode214 as a mask. Thus, source and drain regions 208 a and 208 b are formedin regions that do not overlap the gate electrode 214 formed on thesecond semiconductor layer 208. In this case, a channel region 208 c isdefined between the source and drain regions 208 a and 208 b.

An interlayer insulating layer 220 is formed over the entire surface ofthe substrate 200 including the first electrode 212 and the gateelectrode 214. Contact holes are formed in the interlayer insulatinglayer 220 and the gate insulating layer 210 to expose the first throughthird semiconductor layers 207, 208, and 209. A conductive layer isformed on the substrate 200 including the contact holes and thenpatterned, thereby forming source and drain electrodes 221 and 223 inthe TFT region (a). Then, a data line 225 and a metal 227 which appliesa reference voltage to the third semiconductor layer 209, are formed inthe data line capacitor region (b). Also, a second electrode 229, whichcomes into contact with the first semiconductor layer 207, is formed inthe storage capacitor region (c).

Here, the second semiconductor layer 208, the gate insulating layer 210,the gate electrode 214, the source electrode 221, and the drainelectrode 223 are formed in the TFT region (a) to produce a TFT. The TFTmay be, for example, a driving transistor (M1 of FIG. 4), whichgenerates a driving current, or an emission control transistor (M6 ofFIG. 4), which supplies the driving current to the organic lightemitting diode OLED.

Also, the first semiconductor layer 207, the gate insulating layer 210,the first electrode 212, the interlayer insulating layer 220, and thesecond electrode 229 which is in contact with the first semiconductorlayer 207, are formed in the storage capacitor region (c) to produce astorage capacitor C_(st).

Further, the third semiconductor layer 209, the gate insulating layer210, the interlayer insulating layer 220, the data line 225 are formedin the data line capacitor region (b) to produce a first data linecapacitor C_(data1).

A passivation layer 230 is formed over the entire surface of thesubstrate 200 including the electrodes 221, 223, 225, 227, and 229 thatare formed by patterning the conductive layer. The passivation layer 230may comprise at least one of a silicon oxide (SiO₂) layer, a siliconnitride (SiN_(X)) layer, and a multi-layer thereof. In some embodimentsthe passivation layer 230 is formed of a silicon nitride (SiN_(X))layer, which effectively protects the underlying TFT from gas ormoisture and may be hydrogen-rich to protect incomplete bonding existingin grain boundaries of the poly-Si layer.

A first via hole 232 is formed in the passivation layer 230 to exposethe drain electrode 223 of the TFT.

A planarization layer 235 is formed on the passivation layer 230 toreduce the step height, and may comprise at least one of an organiclayer, such as a benzocyclobutene (BCB) layer, a polyimide layer, and apolyacryl layer.

A second via hole 237 and a third via hole 239 are formed in theplanarization layer 235. The second via hole 237 exposes the drainelectrode 223 of the TFT in the TFT region (a), and the third via hole239 exposes the passivation layer 230 formed on the data line 225 in thedata line capacitor region (b).

A pixel electrode 240 is formed on the planarization layer 235 havingthe second via hole 237 in the storage capacitor region (c) and the TFTregion (a). The pixel electrode 240 is in contact with the drainelectrode 223 that is exposed by the second via hole 237 in the TFTregion (a). Also, since the pixel shown in FIG. 8 is a top-emittingtype, the pixel electrode 240 may be formed of a light-reflectingconductive layer. The light-reflecting conductive layer may comprise atleast one of Ag, Al, Ni, Pt, Pd, and an alloy thereof having a high workfunction. The light-reflecting conductive layer may comprise at leastone of Mg, Ca, Al, Ag, Ba, or an alloy thereof having a low workfunction. In some embodiments, before the pixel electrode 240 is formed,a reflective layer pattern 242 may be further formed, and then the pixelelectrode 240 may be formed thereon using a light-transmittingconductive layer. The light-transmitting conductive layer may compriseat least one of an indium tin oxide (ITO) and indium zinc oxide (IZO)layer. In some embodiments the reflective layer pattern 242 has areflectivity of 60% or higher and comprises at least one of Al, an Alalloy, Ag, an Ag alloy, and an alloy thereof. This reflective layerpattern 242 may be formed spaced apart from the second via hole 237 by apredetermined distance.

A pixel defining layer (PDL) 245 is formed over the entire surface ofthe substrate 200 including the pixel electrode 240. The PDL 245 maycomprise at least one of BCB, acrylic photoresist, phenolic photoresist,and imidic photoresist.

An opening 247 and a fourth via hole 249 are formed in the PDL 245. Theopening 247 exposes at least a portion (emission region) of the pixelelectrode 240 and the fifth via hole 249 exposes the passivation layer230 formed on the data line 225 in the data line capacitor region (b).

An organic emission layer 250 is formed on the region of the pixelelectrode 240 that is exposed by the opening. The organic emission layer250 may be formed by a vacuum deposition process, an inkjet printingprocess, or a laser induced thermal imaging (LITI) process. Further, ahole injection layer, a hole transport layer, a hole blocking layer, anelectron transport layer, or an electron injection layer may be formedon or under the organic emission layer 250. Subsequently, an oppositeelectrode 255 is formed on the entire surface of the substrate 200including the organic emission layer 250 and the PDL 245. The oppositeelectrode 255 may comprise at least one of a light-transmittingconductive layer and a metal reflective layer. The light-transmittingconductive layer may be an ITO or IZO layer or formed of Mg, Ca, Al, Ag,Ba, or an alloy thereof to such a small thickness as to transmit light.

In the storage capacitor region (c) and the TFT region (a), the pixelelectrode 240, the organic emission layer 250, and the oppositeelectrode 255 constitute an organic light emitting diode OLED. Also, thedata line 225, the passivation layer 230, and the opposite electrode 255form a second data line capacitor C_(data2) in the data line capacitorregion (b).

While the organic light emitting diode operates, holes and electrons (orelectrons and holes) are emitted from the pixel electrode 240 and theopposite electrode 255, respectively, and injected into the organicemission layer 250. The holes and electrons combine with each other inthe organic emission layer 250, thus generating excitons. As theexcitons are changed from an excited state to a ground state, theorganic emission layer 250 emits light. The light emitted from theorganic emission layer 250 is reflected by the pixel electrode 240formed of a light-reflecting conductive layer or the reflective layerpattern 242 disposed under the pixel electrode 240 formed of alight-transmitting conductive layer, and passes through the oppositeelectrode 255 formed of the light-transmitting layer to be emitted tothe exterior.

As described above, the pixel according one embodiment includes thefirst data line capacitor C_(data1) obtained by forming the thirdsemiconductor layer 209 under the data line 225. Also, the planarizationlayer 235 and the PDL 245 are etched through the third and/or fourth viaholes 239 and/or 249 in the data line capacitor region (b), so that theopposite electrode 255 and the data line 225 form the second data linecapacitor C_(data) 2 using only the passivation layer 230 as adielectric layer.

Accordingly, the data line capacitor C_(data) has a structure to whichthe first and second data line capacitors C_(data1) and C_(data2) areconnected in parallel about the data line 225. That is,C_(data)=C_(data1)+C_(data2). In applying the pixel structure accordingto one embodiment, the data line capacitor C_(data) has a capacitance of20 to 50 [PF], which is about 16 times more than in the conventionalpixel structure. Therefore, when the pixel driving method using thedemultiplexers is applied according that described above, the gatevoltage Vg of the driving transistor becomes substantially equal to theapplied data voltage Vdata, so that the OLED can display improved grayscale and have substantially uniform luminance.

The capacitance of the data line capacitor C_(data) may be adjusted bycontrolling the size of a via hole formed in an insulating layer, suchas a passivation layer, a planarization layer, or a PDL and the size ofa contact hole via which a semiconductor layer is in contact with ametal.

FIG. 9 is a cross-sectional view of a pixel having a structure toincrease the capacitance of a data line capacitor according to anotherembodiment. In FIG. 9, a pixel region is divided into 3 regions, i.e., aTFT region (a), a data line capacitor region (b), and a storagecapacitor region (c) like in FIG. 8. Here, the same processes asdescribed with reference to FIG. 8 will be briefly described, butdifferent processes will be described in detail.

Referring to FIG. 9, a substrate 200 is prepared to form a pixel region.A buffer layer 205 may be formed on the substrate 200.

First through third semiconductor layers 207, 208, and 209 are patternedover the buffer layer 205. That is, the first semiconductor layer 207 ispatterned in the storage capacitor region (c), the second semiconductorlayer 208 is patterned in the TFT region (a), and the thirdsemiconductor layer 209 is patterned in the data line capacitor region(b).

A gate insulating layer 210 is formed over the entire surface of thesubstrate 200 including the first through third semiconductor layers207, 208, and 209. The gate insulating layer 210 may comprise at leastone of a silicon oxide (SiO₂) layer, a silicon nitride (SiN_(X)) layer,a silicon oxynitride (SiO₂N_(X)) layer, and a multi-layer thereof.

A first electrode 212 of a storage capacitor C_(st) is formed on thegate insulating layer 210 in the storage capacitor region (c) to overlapthe first semiconductor layer 207, and a gate electrode 214 is formed inthe TFT region (a) to overlap the second semiconductor layer 208. Inthis case, while the first electrode 212 and the gate electrode 214 arebeing formed, scan lines (S_(n-1), S_(n), and En of FIG. 4) may also beformed at the same time.

Thereafter, dopants (n⁺ or p⁺ type) are implanted into the secondsemiconductor layer 208 in the TFT region (a) using the gate electrode214 as a mask. Thus, source and drain regions 208 a and 208 b are formedin regions that do not overlap the gate electrode 214 formed on thesecond semiconductor layer 208. In this case, a channel region 208 c isdefined between the source and drain regions 208 a and 208 b.

An interlayer insulating layer 220 is formed over the entire surface ofthe substrate 200 including the first electrode 212 and the gateelectrode 214. Contact holes are formed in the interlayer insulatinglayer 220 and the gate insulating layer 210 to expose the first throughthird semiconductor layers 207, 208, and 209. A conductive layer isformed over the substrate 200 including the contact holes and thenpatterned, thereby forming source and drain electrodes 221 and 223 inthe TFT region (a). Then, a data line 225 and a metal 227, which appliesa reference voltage to the third semiconductor layer 209, are formed inthe data line capacitor region (b). Also, a second electrode 229, whichcomes into contact with the first semiconductor layer 207, is formed inthe storage capacitor region (c).

Here, the second semiconductor layer 208, the gate insulating layer 210,the gate electrode 214, the source electrode 221, and the drainelectrode 223 are formed in the TFT region (a) to produce a TFT. The TFTmay, for example be a driving transistor (M1 of FIG. 4), which generatesa driving current, or an emission control transistor (M6 of FIG. 4),which supplies the driving current to the organic light emitting diodeOLED.

Also, the first semiconductor layer 207, the gate insulating layer 210,the first electrode 212, the interlayer insulating layer 220, and thesecond electrode 229 which is in contact with the first semiconductorlayer 207, are formed in the storage capacitor region (c) to form astorage capacitor C_(st).

Further, the third semiconductor layer 209, the gate insulating layer210, the interlayer insulating layer 220, the data line 225 are stackedin the data line capacitor region (b) to form a first data linecapacitor C_(data1).

A passivation layer 230 is formed over the entire surface of thesubstrate 200 including the electrodes 221, 223, 225, 227, and 229 thatare formed by patterning the conductive layer. The passivation layer 230may comprise at least one of a silicon oxide (SiO₂) layer, a siliconnitride (SiN_(X)) layer, and a multi-layer thereof. Also, in someembodiments the passivation layer 230 may not be formed.

A first via hole 232 and a second via hole 234 are formed in thepassivation layer 230. The first via hole 232 exposes the drainelectrode 223 of the TFT, and the second via hole 234 exposes the dataline 225.

A planarization layer 235 is formed on the passivation layer 230 toreduce the step height, and may be formed of an organic layer. A thirdvia hole 237 is formed in the planarization layer 235 in the TFT region(a) to expose the drain electrode 223 in a region where the first viahole 232 is formed. Also, a fourth via hole 239 is formed in theplanarization layer 235 formed on the data line 225.

A pixel electrode 240 is formed on the planarization layer 235 havingthe third via hole 237 in the storage capacitor region (c) and the TFTregion (a). The pixel electrode 240 is in contact with the drainelectrode 223 that is exposed by the third via hole 237 in the TFTregion (a). Additionally, since the pixel shown in FIG. 9 is atop-emitting type, the pixel electrode 240 may be formed of alight-reflecting conductive layer. In another embodiment, before thepixel electrode 240 is formed, a reflective layer pattern 242 may befurther formed, and then the pixel electrode 240 may be formed using alight-transmitting conductive layer. This reflective layer pattern 242may be spaced apart from the third via hole 237 by a predetermineddistance.

A PDL 245 is formed on the entire surface of the substrate 200 includingthe pixel electrode 240. An opening 247 and a fifth via hole 249 areformed in the PDL 245. The opening 247 exposes at least a portion(emission region) of the pixel electrode 240, and the fifth via hole 249exposes the partially etched planarization layer 235 on the data line225.

An organic emission layer 250 is formed on the pixel electrode 240 thatis exposed by the opening 247. Subsequently, an opposite electrode 255is formed on the entire surface of the substrate 200 including theorganic emission layer 250 and the PDL 245. The opposite electrode 255may comprise at least one of a light-transmitting conductive layer and ametal reflective layer.

In the storage capacitor region (c) and the TFT region (a), the pixelelectrode 240, the organic emission layer 250, and the oppositeelectrode 255 form an organic light emitting diode. Also, the data line225, the planarization layer 235, and the opposite electrode 255 form asecond data line capacitor C_(data2) in the data line capacitor region(b).

As described above, in the pixel according to one embodiment, the firstdata line capacitor C_(data1) is produced by forming the thirdsemiconductor layer 209 under the data line 225. Also, the passivationlayer 230, the planarization layer 235, and the PDL 245 are etchedthrough the second, fourth, and fifth via holes 234, 239 and 249 in thedata line capacitor region (b), so that the opposite electrode 255 andthe data line 225 constitute the second data line capacitor C_(data2)using only the planarization layer 235 as a dielectric layer.

Accordingly, the data line capacitor C_(data) has a structure to whichthe first and second data line capacitors C_(data1) and C_(data2) areconnected in parallel about the data line 225. That is,C_(data)=C_(data1)+C_(data2). In applying the pixel structure accordingto the second embodiment of the present invention, the data linecapacitor C_(data) has a capacitance of 20 to 50 [PF], which is about 16times more than in the conventional pixel structure. Therefore, when thepixel driving method using the demultiplexers is used, the gate voltageVg of a driving transistor becomes substantially equal to the applieddata voltage Vdata, so that the OLED can display exact gray scale andhave uniform luminance.

The capacitance of the data line capacitor C_(data) may be adjusted bycontrolling the size of a via hole formed in an insulating layer, suchas a passivation layer, a planarization layer, or a PDL and the size ofa contact hole via which a semiconductor layer is in contact with ametal layer.

FIG. 10 is a cross-sectional view of a pixel having a structure toincrease the capacitance of a data line capacitor according to yetanother embodiment. In FIG. 10, a pixel region is divided into 3regions, i.e., a TFT region (a), a data line capacitor region (b), and astorage capacitor region (c) like in FIG. 8. Here, the same processes asdescribed with reference to FIG. 8 will be briefly described, butdifferent processes will be described in detail.

Referring to FIG. 10, to form a pixel region according to thisembodiment, a substrate 200 is prepared. A buffer layer 205 may beformed on the substrate 200.

First through third semiconductor layers 207, 208, and 209 are patternedover the buffer layer 205. That is, the first semiconductor layer 207 ispatterned in the storage capacitor region (c), the second semiconductorlayer 208 is patterned in the TFT region (a), and the thirdsemiconductor layer 209 is patterned in the data line capacitor region(b).

A gate insulating layer 210 is formed on the entire surface of thesubstrate 200 including the first through third semiconductor layers207, 208, and 209. The gate insulating layer 210 may comprise at leastone of a silicon oxide (SiO₂) layer, a silicon nitride (SiN_(X)) layer,a silicon oxynitride (SiO₂N_(X)) layer, and a multi-layer thereof.

A first electrode 212 of a storage capacitor C_(st) is formed on thegate insulating layer 210 in the storage capacitor region (c) to overlapthe first semiconductor layer 207, and a gate electrode 214 is formed inthe TFT region (a) to overlap the second semiconductor layer 208. Inthis case, while the first electrode 212 and the gate electrode 214 arebeing formed, scan lines (S_(n-1), S_(n), and E_(n) of FIG. 4) may beformed at the same time.

Thereafter, dopants (n⁺ or p⁺ type) are implanted into the secondsemiconductor layer 208 in the TFT region (a) using the gate electrode214 as a mask. Thus, source and drain regions 208 a and 208 b are formedin regions that do not overlap the gate electrode 214 formed on thesecond semiconductor layer 208. In this case, a channel region 208 c isdefined between the source and drain regions 208 a and 208 b.

An interlayer insulating layer 220 is formed over the entire surface ofthe substrate 200 including the first electrode 212 and the gateelectrode 214. Contact holes are formed in the interlayer insulatinglayer 220 and the gate insulating layer 210 to expose the first throughthird semiconductor layers 207, 208, and 209. A conductive layer isformed over the substrate 200 including the contact holes and thenpatterned, thereby forming source and drain electrodes 221 and 223 inthe TFT region (a). Then, a data line 225 and a metal 227, which appliesa reference voltage to the third semiconductor layer 209, are formed inthe data line capacitor region (b). Also, a second electrode 229, whichcomes into contact with the first semiconductor layer 207, is formed inthe storage capacitor region (c).

Here, the second semiconductor layer 208, the gate insulating layer 210,the gate electrode 214, the source electrode 221, and the drainelectrode 223 are stacked in the TFT region (a) to form a TFT. The TFTmay, for example, be a driving transistor (M1 of FIG. 4), whichgenerates a driving current, or an emission control transistor (M6 ofFIG. 4), which supplies the driving current to the organic lightemitting diode OLED. Also, the first semiconductor layer 207, the gateinsulating layer 210, the first electrode 212, the interlayer insulatinglayer 220, and the second electrode 229, which is in contact with thefirst semiconductor layer 207, are formed such that they overlap in thestorage capacitor region (c) to form a storage capacitor C_(s)t.Further, the third semiconductor layer 209, the gate insulating layer210, the interlayer insulating layer 220, the data line 225 are formedsuch that they overlap in the data line capacitor region (b) to form afirst data line capacitor C_(data1).

A passivation layer 230 is formed over the entire surface of thesubstrate 200 including the electrodes 221, 223, 225, 227, and 229 thatare formed by patterning the conductive layer. The passivation layer 230may comprise at least one of a silicon oxide (SiO₂) layer, a siliconnitride (SiN_(X)) layer, and a multi-layer thereof. Also, in someembodiments the passivation layer 230 may not be formed. A first viahole 232 and a second via hole 234 are formed in the passivation layer230. The first via hole 232 exposes the drain electrode 223 of the TFT,and the second via hole 234 exposes the data line 225.

A planarization layer 235 is formed on the passivation layer 230 toreduce the step height, and may be formed of an organic layer, such as aBCB layer, a polyimide layer, or a polyacryl layer. A third via hole 237is formed in the planarization layer 235 in the TFT region (a) to exposethe drain electrode 223 in a region where the first via hole 232 isformed. Also, a fourth via hole 239 is formed to expose the data line225.

A pixel electrode 240 is formed on the planarization layer 235 havingthe third via hole 237 in the storage capacitor region (c) and the TFTregion (a). The pixel electrode 240 is in contact with the drainelectrode 223 that is exposed by the third via hole 237 in the TFTregion (a). Additionally, since the pixel shown in FIG. 10 is atop-emitting type, the pixel electrode 240 may be formed of alight-reflecting conductive layer. In another embodiment, before thepixel electrode 240 is formed, a reflective layer pattern 242 may befurther formed, and then the pixel electrode 240 may be formed using alight-transmitting conductive layer. This reflective layer pattern 242may be spaced apart from the third via hole 237 by a predetermineddistance.

A PDL 245 is formed on the entire surface of the substrate 200 includingthe pixel electrode 240. An opening 247 and a fifth via hole 249 areformed in the PDL 245. The opening 247 exposes at least a portion(emission region) of the pixel electrode 240, and a portion of the PDL245 is etched by the fifth via hole 249 on the data line 225.

An organic emission layer 250 is formed on the pixel electrode 240 thatis exposed by the opening 247. Subsequently, an opposite electrode 255is formed on the entire surface of the substrate 200 including theorganic emission layer 250 and the PDL 245. The opposite electrode 255may comprise at least one of a light-transmitting conductive layer and ametal reflective layer.

In the storage capacitor region (c) and the TFT region (a), the pixelelectrode 240, the organic emission layer 250, and the oppositeelectrode 255 form an organic light emitting diode. Also, the data line225, the planarization layer 235, and the opposite electrode 255 form asecond data line capacitor C_(data2) in the data line capacitor region(b).

As described above, the pixel according to one embodiment, the firstdata line capacitor C_(data1) is produced by forming the thirdsemiconductor layer 209 under the data line 225. Also, the passivationlayer 230, the planarization layer 235, and the PDL 245 are etchedthrough the second, fourth, and fifth via holes 234, 239 and 249 in thedata line capacitor region (b), and the opposite electrode 255 and thedata line 225 constitute the second data line capacitor C_(data 2) usingonly the PDL 245 as a dielectric layer.

Accordingly, the data line capacitor C_(data) has a structure to whichthe first and second data line capacitors C_(data1) and C_(data2) areconnected in parallel about the data line 225. That is,C_(data)=C_(data1)+C_(data2). In applying the pixel structure accordingto the third embodiment of the present invention, the data linecapacitor C_(data) has a capacitance of 20 to 50 [PF], which is about 16times more than in the conventional pixel structure. Therefore, when thepixel driving method using the demultiplexers is used, the gate voltageVg of a driving transistor becomes substantially equal to the applieddata voltage Vdata, so that the OLED can display exact gray scale andhave uniform luminance.

The capacitance of the data line capacitor C_(data) may be adjusted bycontrolling the size of a via hole formed in an insulating layer, suchas a passivation layer, a planarization layer, or a PDL and the size ofa contact hole via which a semiconductor layer is in contact with ametal layer.

FIG. 11 is a cross-sectional view of a pixel having a structure toincrease the capacitance of a data line capacitor according to yetanother embodiment. In FIG. 11, a pixel region is divided into 3regions, i.e., a TFT region (a), a data line capacitor region (b), and astorage capacitor region (c) like in FIG. 8. Here, the same processes asdescribed with reference to FIG. 8 will be briefly described, butdifferent processes will be described in detail.

Referring to FIG. 11, to form a pixel region according to thisembodiment, a substrate 200 is prepared. A buffer layer 205 may beformed on the substrate 200.

First through third semiconductor layers 207, 208, and 209 are patternedon the buffer layer 205. That is, the first semiconductor layer 207 ispatterned in the storage capacitor region (c), the second semiconductorlayer 208 is patterned in the TFT region (a), and the thirdsemiconductor layer 209 is patterned in the data line capacitor region(b).

A gate insulating layer 210 is formed over the entire surface of thesubstrate 200 including the first through third semiconductor layers207, 208, and 209. The gate insulating layer 210 may comprise at leastone of a silicon oxide (SiO₂) layer, a silicon nitride (SiN_(X)) layer,a silicon oxynitride (SiO₂N_(X)) layer, and a multi-layer thereof.

A first electrode 212 of a storage capacitor C_(st) is formed on thegate insulating layer 210 in the storage capacitor region (c) to overlapthe first semiconductor layer 207, and a gate electrode 214 is formed inthe TFT region (a) to overlap the second semiconductor layer 208. Inthis case, while the first electrode 212 and the gate electrode 214 arebeing formed, scan lines (S_(n-1), S_(n), and E_(n) of FIG. 4) may alsobe formed at the same time.

Thereafter, dopants (n⁺ or p⁺ type) are implanted into the secondsemiconductor layer 208 in the TFT region (a) using the gate electrode214 as a mask. Thus, source and drain regions 208 a and 208 b are formedin regions that do not overlap the gate electrode 214 formed on thesecond semiconductor layer 208. In this case, a channel region 208 c isdefined between the source and drain regions 208 a and 208 b.

An interlayer insulating layer 220 is formed over the entire surface ofthe substrate 200 including the first electrode 212 and the gateelectrode 214. Contact holes are formed in the interlayer insulatinglayer 220 and the gate insulating layer 210 to expose the first throughthird semiconductor layers 207, 208, and 209. A conductive layer isformed over the substrate 200 including the contact holes and thenpatterned, thereby forming source and drain electrodes 221 and 223 inthe TFT region (a). Then, a data line 225 and a metal 227, which appliesa reference voltage to the third semiconductor layer 209, are formed inthe data line capacitor region (b). Also, a second electrode 229, whichcomes into contact with the first semiconductor layer 207, is formed inthe storage capacitor region (c).

Here, the second semiconductor layer 208, the gate insulating layer 210,the gate electrode 214, the source electrode 221, and the drainelectrode 223 are formed in the TFT region (a) to produce a TFT. The TFTmay, for example, be a driving transistor (M1 of FIG. 4), whichgenerates a driving current, or an emission control transistor (M6 ofFIG. 4), which supplies the driving current to the organic lightemitting diode OLED.

Also, the first semiconductor layer 207, the gate insulating layer 210,the first electrode 212, the interlayer insulating layer 220, and thesecond electrode 229, which is in contact with the first semiconductorlayer 207, are formed in the storage capacitor region (c) to form astorage capacitor C_(st). Further, the third semiconductor layer 209,the gate insulating layer 210, the interlayer insulating layer 220, thedata line 225 are stacked in the data line capacitor region (b) to forma first data line capacitor C_(data1).

A passivation layer 230 is formed over the entire surface of thesubstrate 200 including the electrodes 221, 223, 225, 227, and 229 thatare formed by patterning the conductive layer. The passivation layer 230may comprise at least one of a silicon oxide (SiO₂) layer, a siliconnitride (SiN_(X)) layer, and a multi-layer thereof. Also, in someembodiments, the passivation layer 230 may not be formed. A first viahole 232 is formed in the passivation layer 230 to expose the drainelectrode 223 of the TFT.

A planarization layer 235 is formed on the passivation layer 230 toreduce the step height, and may be formed of an organic layer, such as aBCB layer, a polyimide layer, or a polyacryl layer. A second via hole237 is formed in the planarization layer 235 in the TFT region (a) toexpose the drain electrode 223 in a region where the first via hole 232is formed. Also, a third via hole 239 is formed to expose thepassivation layer 230.

A pixel electrode 240 is formed over the entire surface of the substrate200 including the planarization layer 235 in which the second via hole237 and the third via hole 239 are formed. The pixel electrode 240 is incontact with the drain electrode 223 that is exposed by the second viahole 237. Also, the pixel electrode 240 is formed over the passivationlayer 230 that is exposed by the third via hole 239. Further, the pixelelectrode 240 may be formed over the planarization layer 235 if thepassivation layer 230 is not formed. Additionally, since the pixel shownin FIG. 11 is a top-emitting type, the pixel electrode 240 may be formedof a light-reflecting conductive layer. In another embodiment, beforethe pixel electrode 240 is formed, a reflective layer pattern 242 may befurther formed, and then the pixel electrode 240 may be formed using alight-transmitting conductive layer. This reflective layer pattern 242may be spaced apart from the second via hole 237 by a predetermineddistance.

A PDL 245 is formed on the entire surface of the substrate 200 includingthe pixel electrode 240. An opening 247 is formed in the PDL 245 toexpose at least a portion (emission region) of the pixel electrode 240.

An organic emission layer 250 is formed on the pixel electrode 240 thatis exposed by the opening 247. Subsequently, an opposite electrode 255is formed on the entire surface of the substrate 200 including theorganic emission layer 250 and the PDL 245. The opposite electrode 255may comprise at least one of a light-transmitting conductive layer and ametal reflective layer.

In the storage capacitor region (c) and the TFT region (a), the pixelelectrode 240, the organic emission layer 250, and the oppositeelectrode 255 form an organic light emitting diode. Also, the data line225, the passivation layer 230 (and/or the planarization layer 235), andthe opposite electrode 255 form a second data line capacitor C_(data2)in the data line capacitor region (b).

As described above, the pixel according to one embodiment, the firstdata line capacitor C_(data1) is obtained by forming the thirdsemiconductor layer 209 under the data line 225. Also, the passivationlayer 230 and/or the planarization layer 235 are etched through thethird via hole 239 in the data line capacitor region (b), and the pixelelectrode 240 and the data line 225 constitute the second data linecapacitor C_(data2) using only the passivation layer 230 and/or theplanarization layer 235 as a dielectric layer.

Accordingly, the data line capacitor C_(data) has a structure to whichthe first and second data line capacitors C_(data1) and C_(data2) areconnected in parallel about the data line 225. That is,C_(data)=C_(data1)+C_(data2). In applying the pixel structure accordingto the fourth embodiment of the present invention, the data linecapacitor C_(data) has a capacitance of 20 to 50 [PF], which is about 16times more than in the conventional pixel structure. Therefore, when thepixel driving method using the demultiplexers is used, the gate voltageVg of a driving transistor becomes substantially equal to the applieddata voltage Vdata, so that the OLED can display exact gray scale andhave uniform luminance.

The capacitance of the data line capacitor C_(data) may be selected bycontrolling the size of a via hole formed in an insulating layer, suchas a passivation layer, a planarization layer, or a PDL and the size ofa contact hole via which a semiconductor layer is in contact with ametal layer.

FIG. 12 is a circuit diagram of another pixel of the OLED shown in FIG.2.

Referring to FIG. 12, a pixel 110 includes an organic light emittingdiode OLED, which emits light according to a driving current, and apixel driving circuit 111, which supplies the driving current to theorganic light emitting diode OLED. A data voltage Vdata, which is storedin a data line capacitor C_(datamk) during a data writing period, isapplied to the pixel driving circuit 111.

The pixel driving circuit 111 includes a driving transistor M1, aswitching transistor M2, an emission control transistor M3, and astorage capacitor C_(st). The switching transistor M2 is turned on oroff in response to a selection signal applied to a scan line S_(n)connected to a gate terminal and transmits the data voltage Vdata from adata line D_(mk). The driving transistor M1 is connected between a firstvoltage line Vdd and the emission control transistor M3 and has a gateterminal connected to a drain of the switching transistor M2 to generatea driving current corresponding to the data voltage Vdata. The storagecapacitor C_(st) is connected between the first voltage line Vdd and thegate terminal of the driving transistor M1 and maintains the datavoltage Vdata for a predetermined time. The emission control transistorM3 is connected between the driving transistor M1 and the organic lightemitting diode OLED to transmit the driving current to the organic lightemitting diode OLED in response to an emission control signal of anemission control line E_(n) connected to the gate terminal.

Operations of the pixel shown in FIG. 12 will now be described.Initially, the data voltage Vdata is stored in the data line capacitorC_(datamk) during a data writing period. Next, when a selection signalis applied to the scan line S_(n), the switching transistor M2 is turnedon. In this state, the data voltage Vdata stored in the data linecapacitor C_(datamk) is applied to the gate terminal of the drivingtransistor M1 via the switching transistor M2, and electric chargesequivalent to a difference between a first voltage Vdd and the datavoltage Vdata are stored in the storage capacitor C_(st). The drivingtransistor M1 operates as a constant current source due to the firstvoltage Vdd applied to a source and the voltage Vdata applied to a gateand supplies the driving current to the organic light emitting diodeOLED.

In this case, the current supplied to the organic light emitting diodeOLED can be expressed as Equation 3:

I _(OLED) =k(Vgs−Vth)² =k(Vdd−Vdata−Vth)²  (3)

where I_(OLED) is the current supplied to the organic light emittingdiode OLED, Vgs is the voltage between the source and gate of thedriving transistor M1, Vth is the threshold voltage of the drivingtransistor M1, Vdata is the data voltage, and k is a constant.

FIG. 13 is a circuit diagram of yet another pixel of the OLED shown inFIG. 2.

Referring to FIG. 13, a pixel 110 includes an organic light emittingdiode OLED, which emits light according to a driving current, and apixel driving circuit 111, which supplies the driving current to theorganic light emitting diode OLED. A data voltage Vdata, which is storedin a data line capacitor C_(datamk) during a data writing period, isapplied to the pixel driving circuit 111.

The pixel driving circuit 111 includes first through fifth TFTs M1-M5and a storage capacitor C_(st). Here, the first transistor M1 is aswitching transistor, and the fourth transistor M4 is a drivingtransistor. Also, the second transistor M2 is an initializationtransistor, and the third transistor M3 is a compensation transistor,which compensates a threshold voltage of the driving transistor M4.Specifically, the first transistor M1 turns on or off in response to aselection signal applied to an nth scan line S_(n) connected to a gateterminal thereof and transmits or passes the data voltage Vdata from adata line D_(mk) to the third transistor M3. The second transistor M2 isturned on in response to a selection signal applied to an (n−1)th scanline S_(n-1) connected to a gate terminal thereof and initializes thedata voltage Vdata during an (n−1)th frame period. The third and fourthtransistors M3 and M4, which are mirror-type transistors, have commonlyconnected gate terminals, so that a voltage corresponding to thedifference between the data voltage Vdata supplied from the firsttransistor M1 and a threshold voltage of the third transistor M3 isapplied to the gate terminal of the fourth transistor M4. The storagecapacitor C_(st) is connected between a first voltage line Vdd and thegate terminal of the fourth transistor M4 and maintains a data voltageVdata-Vth for a predetermined time. The fifth transistor M15 isconnected between the fourth transistor M4 and the organic lightemitting diode OLED and supplies the driving current to the organiclight emitting diode OLED in response to an emission control signal ofan emission control line E_(n) connected to a gate terminal thereof.

Operations of the pixel shown in FIG. 13 will now be described.Initially, during an initialization operation, when a low-levelselection signal is applied to the (n−1)th scan line S_(n-1), the secondtransistor M2 is turned on, so that the data voltage stored in thestorage capacitor C_(st) during the (n−1)th frame period is initializedvia the second transistor M2.

During a data writing period, a data voltage Vdata is stored in the dataline capacitor C_(datamk).

In a data programming operation, when a low-level selection signal isapplied to the scan line S_(n), the first transistor M1 is turned on,and the mirror-type third and fourth transistors M3 and M4 are also on.Accordingly, a voltage Vdata-Vth_(M3) corresponding to a differencebetween the data voltage Vdata stored in the data line capacitorC_(datamk) and a threshold voltage Vth_(M3) of the third transistor M3is applied to the gate of the fourth transistor M4.

Finally, in an emission operation, when a low-level emission controlsignal is applied to the emission control line E_(n), the fifthtransistor M5 is turned on in response to an emission control signal, sothat a driving current corresponding to the first voltage Vdd applied toa source terminal of the fourth transistor M4 and the voltageVdata-Vth_(M3) applied to the gate terminal thereof is applied to theorganic light emitting diode OLED. Thus, the organic light emittingdiode OLED emits light according to the data signal.

The driving current supplied to the organic light emitting diode OLEDcan be expressed as Equation 4:

I _(OLED) =k(Vgs _(M4) −Vth _(M4))² =k(Vdd−Vdata+Vth _(M3) −Vth _(M4))²=k(Vdd−Vdata)²  (4)

where I_(OLED) is the current supplied to the organic light emittingdiode OLED, Vgs_(M4) is the voltage between the source and gate of thefourth transistor M4, Vth_(M3) is the threshold voltage of the thirdtransistor M3, Vth_(M4) is the threshold voltage of the fourthtransistor M4, Vdata is the data voltage, and k is a constant. Here,when the third transistor M3 is equal in threshold voltage to the fourthtransistor M4, i.e., when Vth_(M3)=Vth_(M4), the threshold voltages ofthe transistors can be compensated, thus the organic light emittingdiode OLED can keep the driving current constant.

FIG. 14 is a circuit diagram of still another pixel of the OLED shown inFIG. 2.

Referring to FIG. 14, a pixel 110 includes an organic light emittingdiode OLED, which emits light according to a driving current, and apixel driving circuit 111, which supplies the driving current to theorganic light emitting diode OLED. A data voltage Vdata, which is storedin a data line capacitor C_(datamk) during a data writing period, isapplied to the pixel driving circuit 111, which includes first throughfifth TFTs M1-M5 and two capacitors C_(st) and C_(vth).

The first transistor M1, which is a driving transistor for driving theorganic light emitting diode OLED, is connected between a first voltageline Vdd and the fourth transistor M4 and controls the driving currentpassing through the organic light emitting diode OLED using a voltageapplied to a gate thereof. The second transistor M2 diode-connects thefirst transistor M1 in response to a selection signal supplied from an(n−1)th scan line S_(n-1).

One node A of the threshold voltage compensation capacitor C_(vth) isconnected to the gate of the first transistor M1, and the storagecapacitor C_(st) and the fifth transistor M5 are connected in parallelbetween the other node B of the threshold voltage compensation capacitorC_(vth) and the first voltage line Vdd. The fifth transistor M5 appliesthe first voltage Vdd to the node B of the threshold voltagecompensation capacitor C_(vth) in response to the selection signalsupplied from the (n−1)th scan line S_(n-1).

The third transistor M3 transmits the data voltage Vdata supplied from adata line D_(mk) to the node B of the threshold voltage compensationcapacitor C_(vth) in response to a selection signal supplied from an nthscan line S_(n). The fourth transistor M4 is connected between the firsttransistor M1 and the organic light emitting diode OLED and connects ordisconnects the first transistor M1 and the organic light emitting diodeOLED in response to an emission control signal supplied from an emissioncontrol line E_(n).

Operations of the foregoing pixel shown in FIG. 14 will now bedescribed. Initially, when a low-level selection signal is applied tothe (n−1)th scan line S_(n-1), the second transistor M2 is turned on sothat the first transistor M1 is diode-connected. Thus, a voltage betweenthe gate and source of the first transistor M1 is changed until itreaches a threshold voltage Vth of the first transistor M1. In thiscase, since the source of the first transistor M1 is connected to thefirst voltage Vdd, a voltage applied to the gate of the first transistorM1, i.e., a voltage applied to the node A of the threshold voltagecompensation capacitor C_(vth) becomes a difference between the firstvoltage Vdd and the threshold voltage Vth. Also, the fifth transistor M5is turned on so that the first voltage Vdd is applied to the node B ofthe storage capacitor C_(vth), thus a voltage V_(Cvth) charged in thethreshold voltage compensation capacitor C_(vth) can be expressed asEquation 5:

V _(Cvth) =V _(B) −V _(A) =Vdd−(Vdd−Vth)=Vth  (5)

where V_(Cvth) is the voltage charged in the capacitor C_(vth), V_(A) isthe voltage applied to the node A of the capacitor C_(vth), and V_(B) isthe voltage applied to the node B of the capacitor C_(vth).

Next, during a data writing period, the data voltage Vdata is stored inthe data line capacitor C_(datamk) via the data line D_(mk). Thereafter,when a low-level selection signal is applied to the nth scan line S_(n),the third transistor M3 is turned on so that the data voltage Vdata isapplied to the node B. Also, since a voltage corresponding to thethreshold voltage Vth of the first transistor M1 is charged in thethreshold voltage compensation capacitor C_(vth), a voltagecorresponding to a difference between the data voltage Vdata and thethreshold voltage Vth of the first transistor M1 is applied to the gateof the first transistor M1.

Finally, the fourth transistor M4 is turned on in response to alow-level signal supplied from the emission control line E_(n), so thata current I_(OLED) according to a gate-source voltage V_(GS) of thefirst transistor M1 is applied to the organic light emitting diode OLED.Thus, the organic light emitting diode OLED emits light according to theapplied data.

The current I_(OLED) supplied to the organic light emitting diode OLEDcan be expressed as Equation 6:

I _(OLED) =k(Vgs−Vth)² =k(Vdd−Vdata+Vth)−Vth ² =k(Vdd−Vdata)²  (6)

where I_(OLED) is the current supplied to the organic light emittingdiode OLED, Vgs is the voltage between the source and gate of the firsttransistor M1, Vth is the threshold voltage of the first transistor M1,Vdata is the data voltage, and k is a constant. As described above,since the current I_(OLED) supplied to the organic light emitting diodeOLED is determined by the first voltage Vdd and the data voltage Vdata,luminance non-uniformity of the driving transistor M1 caused by adifference in threshold voltage is resolved.

As described above, the OLED can reduce the number of output lines andthe production cost because data signals supplied from one output linecan be divided and applied to a plurality of data lines usingdemultiplexers.

Also, voltages corresponding to data signals are sequentially charged indata line capacitors and the charged voltages are applied to pixels atthe same time, so that the OLED can display an image with uniformluminance.

Further, a scan period for which a scan signal is supplied does notoverlap a data writing period for which a data signal is supplied, thusthe OLED can stably display an image. In addition, as the capacitance ofa data line capacitor formed in a data line is much greater than thecapacitance of a storage capacitor, the OLED can display exact grayscale and have uniform luminance.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the device or process illustrated may be made bythose skilled in the art without departing from the scope of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers. Additionally certain features may be practiced in combinationsnot specifically described in any one embodiment discussed herein.

What is claimed is:
 1. An organic light emitting display (OLED)comprising: a substrate; a storage capacitor region, a thin filmtransistor region, and a data line capacitor region each formed on thesubstrate; a storage capacitor formed in the storage capacitor region,the storage capacitor comprising: a first semiconductor layer formed onthe substrate; a gate insulating layer formed on the first semiconductorlayer; a first electrode formed on the gate insulating layer; aninterlayer insulating layer formed on the first electrode; and a secondelectrode formed on the interlayer insulating layer, wherein the secondelectrode is electrically connected to the first semiconductor layer; athin film transistor formed in the thin film transistor region, the thinfilm transistor comprising: a second semiconductor layer formed on thesubstrate; a gate insulating layer formed on the second semiconductorlayer; a gate electrode formed on the gate insulating layer; a sourceelectrode formed on the gate insulating layer; and a drain electrodeformed on the gate insulating layer; a first data line capacitor formedin the data line capacitor region, the first data line capacitorcomprising: a third semiconductor layer formed on the substrate; a gateinsulating layer formed on the third semiconductor layer; an interlayerinsulating layer formed on the gate insulating layer; and a data lineformed on the interlayer insulating layer; an organic light emittingdiode formed on the storage capacitor and the thin film transistor andcomprising: a pixel electrode connected to one of the source and drainelectrodes; an organic emission layer formed on the pixel electrode; andan opposite electrode formed on the storage capacitor, the thin filmtransistor, and the first data line capacitor; and a second data linecapacitor formed on the data line capacitor, the second data linecapacitor comprising: the data line; an insulating layer formed over thedata line; and the pixel electrode.
 2. The OLED according to claim 1,wherein the insulating layer of the second data line capacitor comprisesa passivation layer comprising at least one of a silicon oxide (SiO₂)layer, a silicon nitride (SiN_(X)) layer, and a multi-layer thereof. 3.The OLED according to claim 2, wherein a third data line capacitorcomprises the first and second data line capacitors.
 4. The OLEDaccording to claim 1, wherein the insulating layer of the second dataline capacitor comprises a planarization layer, comprising at least oneof a benzocyclobutene (BCB) layer, a polyimide layer, and a polyacryllayer.
 5. The OLED according to claim 4, wherein a third data linecapacitor comprises the first and second data line capacitors.
 6. TheOLED according to claim 5, wherein the third data line capacitor has alarger capacitance than the storage capacitor.
 7. The OLED according toclaim 6, wherein the third data line capacitor has a capacitance ofabout 20 pF to about 50 pF.
 8. The OLED according to claim 7, whereinthe capacitance of the third data line capacitor depends at least inpart on at least one of the size of a contact hole, the size of a viahole, and the thickness of at least one of the passivation layer, theplanarization layer, and the pixel defining layer.
 9. An organic lightemitting display (OLED) comprising: a substrate; a storage capacitorformed in a first region of the substrate; a thin film transistor formedin a second region of the substrate; a first data line capacitor formedin a third region of the substrate; an organic light emitting diodeformed on the storage capacitor and the thin film transistor; and asecond data line capacitor formed on the data line capacitor, the seconddata line capacitor comprising: the data line; and the pixel electrode.